Short Control Channel Element (scce) to Short Resource Element Groups (sreg) Mapping for Short Physical Downlink Control Channel (spdcch)

1. A method implemented in a User Equipment, UE, comprising: receiving a communication from a base station; determining a mapping between one or more Short Control Channel Elements, SCCEs, and corresponding Short Resource Element Groups, SREGs, for the communication from the base station based on a demodulation scheme used for the communication from the base station; and processing the communication from the base station based on the mapping between the one or more SCCE and the corresponding SREG for the communication from the base station; wherein determining the mapping between the one or more SCCE and the corresponding SREG comprises: determining that the demodulation scheme used for the communication from the base station is a Cell Specific Reference Signal, CRS; and in response, determining the mapping between the one or more SCCE and the corresponding SREG to achieve high frequency diversity; wherein determining the mapping between the one or more SCCE and the corresponding SREG to achieve the high frequency diversity comprises one of the group consisting of: (1) for SREG based localized mapping within a 1os and 2os CRS-based Short Physical Downlink Control Channel, SPDCCH, the SREGs corresponding to an SCCE index k are given by the following definition: k * N sREG sCCE + i ; where k=0, . . . , N sCCE −1, N sCCE is the number of SCCEs in an SPDCCH Resource Block, RB, set, i=0, . . . , N sREG/sCCE −1, and N sREG/sCCE is the number of SREGs per SCCE; and (2) for SREG based distributed mapping in a 2os CRS-based Short Physical Downlink Control Channel, SPDCCH, the SREGs corresponding to an SCCE index k are given by the following definition: kmod ⁢ N s ⁢ C ⁢ C ⁢ E / O ⁢ S + ⌊ k N s ⁢ C ⁢ C ⁢ E / O ⁢ S ⌋ * N s ⁢ R ⁢ E ⁢ G OS + i * N s ⁢ C ⁢ C ⁢ E / O ⁢ S where k=0, . . . , N sCCE −1, N sCCE is the number of SCCEs in the SPDCCH RB set, i=0, . . . , N sREG/sCCE −1, N sCCE/OS is the number of SCCEs per Orthogonal Frequency Division Multiplexing, OFDM, symbol within the SPDCCH RB set; N s ⁢ C ⁢ C ⁢ E / O ⁢ S = ⌊ N s ⁢ R ⁢ E ⁢ G / O ⁢ S N s ⁢ R ⁢ E ⁢ G / s ⁢ C ⁢ C ⁢ E ⌋ ; N sREG/OS is the number of SREGs per OFDM symbol and N sREG/sCCE is the number of SREGs per SCCE.

2. The method of claim 1 wherein determining the mapping between the one or more SCCE and the corresponding SREG to achieve the high frequency diversity comprises determining the SREG corresponding to the SCCE as selected in a distributed manner along the SPDCCH RB set as well as only from 1 OFDM symbol.

3. The method of claim 2 wherein determining the mapping between the one or more SCCE and the corresponding SREG to achieve the high frequency diversity comprises: for the distributed SCCE to SREG mapping in a 1os CRS-based Short Physical Downlink Control Channel, SPDCCH, the SREGs corresponding to an SCCE index k are given by the following definition: k + i * ⌊ N s ⁢ R ⁢ E ⁢ G t ⁢ o ⁢ t N s ⁢ R ⁢ E ⁢ G / s ⁢ C ⁢ C ⁢ E ⌋ where k=0, . . . , N sCCE −1, N sCCE is the number of SCCEs in an SPDCCH Resource Block, RB, set, i=0, . . . , N sREG/sCCE −1, N sREG tot is the total number of SREGs in the SPDCCH RB set, and N sREG/sCCE is the number of SREGs per SCCE.

4. The method of claim 1 wherein N sREG/sCCE is 4 for a CRS-based SPDCCH where N sREG/sCCE is the number of SREGs per SCCE.

5. The method of claim 1 wherein N sREG/sCCE is 4 for a CRS-based SPDCCH.

6. The method of claim 1 wherein determining the mapping between the one or more SCCE and the corresponding SREG comprises: determining that the demodulation scheme used for the communication from the base station is a Demodulation Reference Signal, DMRS; and in response, determining the mapping between the one or more SCCE and the corresponding SREG based on the demodulation scheme used for the communication from the base station is the DMRS.

8. The method of claim 7 wherein N sREG/sCCE is 4 for the 2os DMRS-based SPDCCH.

9. The method of claim 7 wherein N sREG/sCCE is 6 for the 3os DMRS-based SPDCCH.

10. The method of claim 1 further comprising: for an aggregation level higher than one, the SCCEs corresponding to a distributed Demodulation Reference Signal, DMRS,-based SPDCCH candidate m within the SPDCCH RB set of the UE is defined as follows: Y p , k L + m + i * N sCCE L where Y p,k L is an SCCE starting offset of the UE configured by higher layer signaling, i=0, . . . , L−1; L is the aggregation level and is higher than one; N sCCE is the total number of SCCEs in the SPDCCH RB set; m=0, . . . , M L −1; and M L is the number of SPDCCH candidates per aggregation level L.

11. The method of claim 1 wherein receiving the communication from the base station comprises receiving the communication from the base station on an SPDCCH.

12. A User Equipment, UE, configured to communicate with a base station, the UE comprising a radio interface and processing circuitry configured to: receive a communication from the base station; determine a mapping between one or more Short Control Channel Elements, SCCEs, and corresponding Short Resource Element Groups, SREGs, for the communication from the base station based on a demodulation scheme used for the communication from the base station; and process the communication from the base station based on the mapping between the one or more SCCE and corresponding SREG for the communication from the base station; wherein determining the mapping between the one or more SCCE and the corresponding SREG comprises the processing circuitry being configured to: determine that the demodulation scheme used for the communication from the base station is a Cell Specific Reference Signal, CRS; and in response, determine the mapping between the one or more SCCE and the corresponding SREG to achieve high frequency diversity; wherein determining the mapping between the one or more SCCE and the corresponding SREG to achieve the high frequency diversity comprises one of the group consisting of: (1) for SREG based localized mapping within a 1os and 2os CRS-based Short Physical Downlink Control Channel, SPDCCH, the SREGs corresponding to an SCCE index k are given by the following definition: k * N sREG sCCE + i ; where k=0, . . . , N sCCE −1, N sCCE is the number of SCCEs in an SPDCCH Resource Block, RB, set, i=0, . . . , N sREG/sCCE −1, and N sREG/sCCE is a number of SREGs per SCCE; and (2) for SREG based distributed mapping in a 2os CRS-based Short Physical Downlink Control Channel, SPDCCH, the SREGs corresponding to an SCCE index k are given by the following definition: kmod ⁢ N s ⁢ C ⁢ C ⁢ E / O ⁢ S + ⌊ k N s ⁢ C ⁢ C ⁢ E / O ⁢ S ⌋ * N s ⁢ R ⁢ E ⁢ G OS + i * N s ⁢ C ⁢ C ⁢ E / O ⁢ S where k=0, . . . , N sCCE −1, N sCCE is the number of SCCEs in the SPDCCH RB set, i=0, . . . , N sREG/sCCE −1, N sCCE/OS is the number of SCCEs per Orthogonal Frequency Division Multiplexing, OFDM, symbol within the SPDCCH RB set; N sCCE / OS = ⌊ N sREG / OS N sREG / sCCE ⌋ ; N sREG/OS is the number of SREGs per OFDM symbol and N sREG/sCCE is the number of SREGs per SCCE.